Question:
The concept of chromosomal non-disjunction was given by-
The concept of chromosomal non-disjunction was given by-
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Don't confuse the members of Morgan's lab:
Morgan: Sex linkage.
Sturtevant: First genetic map.
Muller: X-ray induced mutations.
Bridges: Non-disjunction and Genic Balance theory.
Morgan: Sex linkage.
Sturtevant: First genetic map.
Muller: X-ray induced mutations.
Bridges: Non-disjunction and Genic Balance theory.
Updated On: Aug 24, 2026
- T. H. Morgan
- A. H. Sturtevant
- H. E. Muller
- C. B. Bridges
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The Correct Option is D
Solution and Explanation
Step 1: Understanding the Question:
The question identifies the scientist who first described the phenomenon where chromosomes fail to separate correctly during cell division.
Step 2: Detailed Explanation:
• Calvin B. Bridges: He was a student of T.H. Morgan and a key member of the famous "Fly Room" at Columbia University.
• The Discovery: While studying the inheritance of the white-eye mutation in Drosophila melanogaster, Bridges noticed rare exceptions to the expected sex-linked inheritance patterns.
• Mechanism: He hypothesized that these exceptions occurred because the X chromosomes sometimes failed to separate during meiosis in the female parent. This phenomenon is called "Non-disjunction".
• Primary Non-disjunction: Occurs in a normal diploid individual.
• Secondary Non-disjunction: Occurs in individuals that already have an abnormal chromosome number (like XXY females).
• Historical Significance: Bridges' work provided the definitive experimental proof of the "Chromosome Theory of Inheritance". By showing that abnormal chromosome behavior perfectly correlated with abnormal trait inheritance, he proved that genes must reside on chromosomes.
Final Answer:
The concept of chromosomal non-disjunction was developed and proven by C.B. Bridges in 1916.
The question identifies the scientist who first described the phenomenon where chromosomes fail to separate correctly during cell division.
Step 2: Detailed Explanation:
• Calvin B. Bridges: He was a student of T.H. Morgan and a key member of the famous "Fly Room" at Columbia University.
• The Discovery: While studying the inheritance of the white-eye mutation in Drosophila melanogaster, Bridges noticed rare exceptions to the expected sex-linked inheritance patterns.
• Mechanism: He hypothesized that these exceptions occurred because the X chromosomes sometimes failed to separate during meiosis in the female parent. This phenomenon is called "Non-disjunction".
• Primary Non-disjunction: Occurs in a normal diploid individual.
• Secondary Non-disjunction: Occurs in individuals that already have an abnormal chromosome number (like XXY females).
• Historical Significance: Bridges' work provided the definitive experimental proof of the "Chromosome Theory of Inheritance". By showing that abnormal chromosome behavior perfectly correlated with abnormal trait inheritance, he proved that genes must reside on chromosomes.
Final Answer:
The concept of chromosomal non-disjunction was developed and proven by C.B. Bridges in 1916.
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